Plants and Society – 03-55-208

Administrative Details:

Lecture Times: Tuesday and Thursday 11:30-12:50

Lecture Room: 361 Dillon Hall

Instructor: Dr. I. Michael Weis Room 202 Biology Building phone: ext. 2724 email: mweis@uwindsor.ca Office hours: T, Th afternoons ~2-4PM

Graduate Assistant: David YurkowskiCounselling/Assistance hours: TBA

Required Text: Plants and Society (2006) Levetin, E. and K. McMahon (4th Edition). McGraw-Hill, Toronto, ON.

Course Website: follow these links www.uwindsor.ca/courses Science

Biology 55-208 Course website

Here you will find the course outline, readings, and Powerpoint slide set for each lecture as early as possible.

Exams, marks and marking policy

• Mid-term Exam (25%) tentative date Feb. 17

• Course Project (combined 30%) (comprised of a research paper (20%) based on the scientific

literature, leading to development of Poster for presentation)

(5% for participation in Poster Session, 5% for poster quality) poster session date TBA

Bonus Mark (2%) for bringing snacks to the Poster Session

• Final Exam (40%)

Both exams will be comprised of multiple choice (and other questions of various types requiring answer choice), short answer (10-25 word answers), and a small number of essay questions.

Course Topics

• Basics of Plant Biology

• Plants as food

• Plants as spice, stimulants and beverages

• Plants as medicines

• Plants for fibre, oils, building materials etc.

• Plants for aesthetics, habitat

• Plant Biotechnology

Cosmology and The Origin of Life

Science now believes the universe as we know it originated in a “Big Bang” approximately 14 BYBP.

Very early on stars originated by the accretion of matter. Lesser amounts of matter in the general vicinity of our sun accreted into the planets (initially into small lumps called planetismals, then growing larger by collisions with asteroids, meteorites or smaller lumps and by gravitational attraction of nearby mass). Earth was initially formed 4-5 BYBP.

When earth finally cooled to a surface temperature <100°C, the energy of volcanic eruptions, lightning, intense UV, cosmic radiation, and radioactive decay caused the formation of the basic molecules of life – amino acids, nucleosides, fatty acids, and simple carbohydrates.

The atmosphere was also important to formation of these molecules: it consisted of CO2, H2O, N2, CH4,

and NH3, possibly H2 and H2S, but no O2.

Amino acids and nucleic acids were joined together abiotically. The various molecules of life were accumulated together, with various pre-life ‘cellular’ assemblies (called protobionts).

The Miller-Urey experiments showed that all the basic monomer units could be formed abiotically.

Sidney Fox demonstrated that short chain polypeptides could form abiotically from amino acid monomers through dehydration of amino acid solutions on hot rocks. Fox also showed that simple, proteinoid microspheres could spontaneously form. Others showed that lipid-based microcells, called liposomes would form. Neither of these incorporates the characteristics by which we define life.

A.I. Oparin showed that completely dissociated cellular components spontaneously re-organized into what he called coacervates.

Coacervates have many of the properties of life. They:

1.Accumulate monomers and polymers from solution and grow

2.Divide (though only by budding off portions of the ‘cell’

3.Decompose glucose (one form of metabolism)

4.Trap energy (a primitive form of electron transport)

5.Have the potential for self-growth (capable of some RNA and protein synthesis)

6.Have the potential to undergo a kind of selection

So, are they “living cells”?

According to Cech and Altman, RNA was probably the first catalyst for protein and nucleic acid synthesis. The first successful, replicating cells, however, had DNA, not RNA. Why? (think of molecular stability, necessary in the harsh, primitive environment and the requirement for at least relatively faithful inheritance)

Whichever protobionts occurred, they were probably present approximately 4 BYBP.

This is an Australian stromatolite. The layers are where fine sediment has stuck to ‘sticky’ prokaryotic cells.

The oldest accepted fossil evidence of cellular life dates back 3.5 billion years. Chemosynthetic bacteria, found in stromatolites from western Australia, date to around 3.5 – 3 BYBP.

What are the characteristics these cells had to possess to be considered living?

1. the capacity for growth and reproduction

2. the ability to respond to their environments

3. the ability to adapt and evolve

4. the ability to metabolize – cellular respiration and (for some) photosynthesis

5. structural (cellular) organization

6. organic composition (based on proteins, nucleic acids, proteins and lipids)

The first primitive Archaea (anaerobic, non-photosynthetic, initially probably not even chemosynthetic) are evident around 3.8 – 3.5 BYBP. They were clearly present in fossils in chert and in stromatolites by 3 BYBP.

Non-photosynthetic, anaerobic prokaryotes (but chemosynthetic, with sulfur-based chemosynthesis) dominated life until ~2.8 BYBP, when photosynthetic bacteria evolved.

Prokaryotes were the only life forms until ~1.5 BYBP, when eukaryotes appeared.

Photosynthetic bacteria (cyanobacteria) and, later, photosynthetic eukaryotes drastically changed the earth’s atmosphere. How?

By releasing free oxygen into the atmosphere. Many anaerobes are intolerant of free oxygen. Other forms of life could evolve (consumers) once oxygen was available to support respiratory metabolism.

Aerobic metabolism produces far more energy per molecule of glucose than does fermentation.

A question for discussion: Do viruses constitute living organisms?

Go through the conditions that characterize life. Does a virus fit all these criteria? Does it have, in and of itself, the ability to grow and reproduce or metabolize?

There are alternative ‘definitions’ of life that might include viruses: Any entity that exhibits counter-entropy and self-replication. Do viruses fit this definition?

This course is about plants. The current view is to separate life into three Domains: Archaea, Bacteria, and Eukarya,

then subdivide Eukarya into: Protista, Fungi, Plantae and Animalia.

What are the characteristics that permit us to separate Plantae from the other domains and sub-domains?

Plant cells are encased within cell walls made largely of cellulose. These are from onion epidermis.

Are cellulose cell walls sufficient to distinguish plants from all other living organisms? No!

Plants are photosynthetic. Inside their cells are plastids called chloroplasts.

Is the presence of photosynthetic membranes sufficient to distinguish plants from other types of living organisms? No!

Cell walls are present in some prokaryotic cells and in fungi. Membrane-bound photosynthetic pigments occur in cyanobacteria.

Even chloroplasts are not exclusively present in plantae. They are also present in photosynthetic protists.

Plants are multicellular, photosynthetic, eukaryotes. Even this is not a perfect discrimination, since there are large kelps that are usually classed in the Protista, but are eukaryotic and photosynthetic.

Let’s continue as if we clearly know what plants are, and consider more about their structure…

How big are plant cells compared to bacteria and animal cells?

As a eukaryotic cell, plant cells have a membrane-enclosed nucleus, as well as other membrane-enclosed organelles. The largest organelle is frequently the empty-looking vacuole.

pits with plasmodesmata

Middle lamella

Let’s look on more detail at some of the key organelles. First, the chloroplast…

Photosynthetic pigments (and other pigments) are located on thylakoid membranes, stacked into grana. Grana are interconnected, embedded in stroma. There are two membranes surrounding the internal structure of the chloroplast.

Why are there two membranes surrounding chloroplasts?

The theory developed by C. Mereschkovsky and Lynn Margulis is of serial endosymbiosis. Plastids (mitochondria and chloroplasts) originated as independent prokaryotes that were engulfed by and came to live within larger cells as symbionts. The outer of the two membranes is the cell membrane of the host cell; the inner membrane is the prokaryotic membrane of the prokaryotic plastid.

Both the structures and composition of the membranes and the small ribosomal subunit RNA sequence support this theory.

There are more pigments than chlorophyll inside chloroplasts. What are they, and how are they visible?

In the fall, when chlorophyll breaks down, the phycoerythrin and phycocyanin are visible as the reds and yellows of fall leaves.

Moving on, the objective is to understand photosynthesis. First, the anatomy of a leaf (in particular, one from a C3 plant)…

Leaf water relations and access to atmospheric CO2 are controlled by stomates – openings in the leaf surface which have guard cells that can close or open the stomate. When guard cells are turgid (well hydrated), stomates are open. When guard cells are flaccid (low water level), stomates close.

Water relations are critical to plant growth and survival. Plants have adapted different strategies in different environments…

In cool temperate regions, plants have the structure and photosynthesis you are probably familiar with, called C3. Both light and dark reactions occur in the mesophyll of the leaf. Sugars are then transported to and through phloem.

In warmer, dryer habitats many plants have adapted a C4 structure and physiology. Here the light reactions and carbon fixation occur in the mesophyll, but the reactions that convert fixed carbon into sugars occur in the bundle sheath, protected from herbivores by tough lignin and silica.

In C4 plants, CO2 is concentrated via addition to PEP (phosphoenolpyruvate) by PEP carboxylase to form malate, which is then transported to bundle sheath cells, where it is released and available for photosynthesis. This makes C4 plants 3-4x more efficient under hot dry conditions, but they have little advantage in moderate climates.

There is one more major form of photosynthesis, called CAM (for Crassulacean Acid Metabolism). It occurs in succulent desert plants and cacti. In CAM plants stomata are closed during days (the thermal stress would cause loss of too much water to transpiration), but open at night. CO2 is fixed at night into 4-carbon molecules (like C4 photosynthesis), and the light reactions and Calvin-Benson cycle reactions occur during the day with stomates closed.

More about photosynthesis later.